Removed the front round crossmember that ran under the stock
clutch housing. After the engine was in its final location,
relocated and welded it back in.
Removed the cross bar at the front of the heater shelf. Removed
the diagonal supports that run from the shock mounting area to
the heater shelf. Shortened these to clear the headers and welded
back in.
Modified the inner fenders to clear the headers and allow better
air flow. Cut out 2 to 3 inches of sheet metal at the bottom of
the inner fenders by the headers. This allowed for better airflow
when the car is going over 35mph but doesn't help much in stop and go.
Cut the front frame extension assembly and widened it to clear the
bottom of the radiator. Cut the radiator duct panel forward (about 4.5")
to clear the radiator and the electric puller fan.
Cut the floorboard brackets near the tunnel, fabricate, relocate
and weld in new brackets when fitting up the engine and tranny.
Widened the stock tunnel to clear the tranny.
Rolled the steering rack down toward the rear of the car. Cut a notch
in the frame crossmember and welded in a piece of sheet metal to fill
in the notch.

Tips:

Don't cut up a good MGA. I restored mine from two junk and very rusty parts cars.